Small hole drilling machine



y 1959 I B. E. FRANK ETAL 2,885,914

SMALL HOLE DRILLING MACHINE Filed Oct. 23, 1957 3 Sheets-Sheet 1 May 12,1959 B. E. FRANK' ETAL SMALL HOLE DRILLING MACHINE 3 Sheets-Shet 2 FiledOct. 25, 1957 May 12, 1959 B. E. FRANK ETAL SMALL nous DRILLING MACHINEFiled Oct. 25. 1957' 3 SheetsSheet 5 H TOCNE Y United States PatentSMALL HOLE DRILLING MACHINE Bernard E. Frank, Marlin E. Hazen, and FayH. Stroud,

Rochester, N.Y., assignors to General Motors Corporation, Detroit,Mich., a corporation of Delaware Application October 23, 1957, SerialNo. 691,923.

2 'Claims. (Cl. 7732.4)

The invention relates to drilling machines and more particularly tomachines for drilling small holes. When small holes are being drilled ina workpiece, care must be taken to prevent drill breakage. This hazardis always present due to the use of small drills which are normallyoperated at high speeds. These drills are usually operated at a speedonly slightly below the drill breaking point. Many of the materialsbeing drilled, particularly castings, are subject to having relativelyhard spots scattered throughout the material. When a drill operating atoptimum speed hits a hard spot of this type, it may be easily brokenunless the hard spot is treated with care. An experienced drill operatorwill, with a very light touch, back oil the drill and cause it to peckslightly up and down with the drill rotating until the hard spot isbroken through. He will then proceed with the drilling operation. Inorder to perform operations of this type, a" highly skilled operatormust be used and he must be vigilant to prevent an undue amount of drillbreakage and scrappingof the workpieces.

A machine embodying the invention accomplishes the same result as thataccomplished by the experienced operator when encountering a hard spot.It causes. the feeding action of the drill to be interrupted andintroduces a pecking action which is continued until the hard spotencountered is broken through. The machine then proceeds with thedrilling operation as if the hard spot'had not been encountered. Thispecking action is obtained only when hard spots are encountered and maybe repeated any number of times depending'upon the number of hard spotsengaged by the drill. The pecking action will not take place so long ashard spots are not encountered.

In the drawings: I

Figure 1 schematically shows a drilling machine embodying the inventionwith the machine in the inoperative position; 7

Figure 2 shows the controls for the machine of Figure Figure 3 shows themachine in the operative position while drilling a workpiece;

Figure 4 shows the controls for-the machine as illustrated in Figure 3;

Figure 5 shows the machine during the pecking action; and

Figure 6 showsthe controls for the machine illustrated in Figure 5. 7

Referring now to the machine and controls therefor, along bar type lever10 is supported on a fulcrum 12", the lever being adjustablycounterweighted by counterweights 14. These weights are slidable alongbar 10 adjacent one end to vary the load on the drill head for differentdrilling operations. The drill motor 16 is suspended from the bar 10 andis furnished with a drill chuck 18 holding a drill 20. The workpiece 22is positioned under drill 20 so that it may be drilled as desired.

The end 24 of bar 10 may be supported when in the inoperative positionby a movable support such as cantiice lever spring. 26. When the bar issupported by spring 26, drill 20 is positioned above workpiece 22 and isprevented from engaging the workpiece. An electric motor 28 driveseccentric cam 30 through appropriate gear reduction. Cam 30 ispositioned. underneath bar 10 at a point intermediate drill motor 16 andthe bar end 24. When cam 30 is rotated in a counterclockwise direction,it engages bar 10 and moves the bar up and down to obtain the desireddrill pecking action.

A feed cam. 32 may be driven by motor 34 through appropriate gearreduction. This. camdetermines the maximum feed rate of the drill 20through the workpiece. This feed rate is preferably coordinated with thedrill speed. so that a maximum amount of material may be removed withina given time while giving due consideration to the life of the drill. Aspring loaded cam follower plunger 36. is secured to bar 10 at point 38intermediate drill motor 16 and the bar end 24. It may be locatedadjacent but spaced. from cam 30. Plunger 36 is biased against cam 32 byspring 40 so that. the plunger is n01"- mally engaged with the. cam andthe spring is normally; compressed: to a predetermined position. Plunger36 is. connected with tandem switch 42 and actuates the switch as" willbe explained below. Tandem switch 42 is pref.- erably a micro switch.Only slight movement of plunger 36'. is required to actuate it.

A. manually controlled switch 44 is provided adjacent a source ofelectricity 46 to control the entire operation of the mechanism. Whilethe source of electricity is illustrated diagrammatically as a battery,it may of course be any source including power supply lines normallyavailable in a shop. Manual switch 44 will start the entire drillingcycle when it is closed.

Three circuits are connected to switch 44. Circuit 48 controls motor 34andv includes contacts 50 of a threecontact switch 52 and contacts 54 oftandem switch 42. Circuit 56 includes contacts 58 of switch 52 andcontacts 60 of switch 42 and controls motor 28. Circuit 62 includescontacts 64 of switch 52 and controls the drill motor 16. Switch 52 hasits contacts 50, 58 and 64 closed when bar 10 is moved off springsupport 26 and lowered until drill 20 is immediately adjacent theworkpiece 22.

In. the inoperative position shown in Figures 1 and 2, drill 22 ispositioned above workpiece 22, cam 30 is in the horizontal positionillustrated with its high point 66 in a plane substantially parallel tothe axis of rotation of the cam. Bar. 10 has its end 24 resting onspring 26. Plunger 36 is engageable with the eccentric cam 32 at itshigh point 68. All of the contacts of switch 52' are opened and microswitch 42 has contact 54 closed and contact 60 opened. Thus none of themotors are energized and the machine is at rest. The workpiece may beremoved and replaced with the machine in this position.

In order to operate the machine, manual switch 44 is closed and bar 10is removed from spring support 26. The bar is permitted to pivot aboutfulcrum 12 until all of the contacts of switch 52 are closed. Bar 10 isnormally permitted to pivot in this direction by proper adjustment ofcounterweights 14 so that the counterweights do not entirely balance themachinery supported by the portion of the bar opposite thecounterweights. When contact 50 of switch 52 is closed, circuits 48 and62 are energized, thus energizing drill motor 16 and cam motor 34. Cammotor 34 is energized since contacts 54 of switch 42 are normallyclosed. Cam 32 begins to rotate in a clockwise direction as isillustrated in Figure 3. The machine and the controls are now in theposition shown in Figures 3 and 4. Bar 10 and the dependent structureincluding drill motor 16 are supported on cam 32 by spring loadedplunger 36. They are gradually lowered by the action of the cam obtainedby its profile and rotation. As cam 32 rotates clockwise, the end ofplunger I 36 approaches the rotating axis of the cam, thus permittingthe drill motor to turn the drill through the workpiece at its maximumpermissible rate.

If and when a hard spot is encountered in the workpiece being drilled,the additional support offered the mechanism by the hard spot will causethe spring biased plunger 36 to be relieved of a portion of itssupporting load. The plunger will thus be moved slightly to actuatemicro switch 42. When this switch is actuated, contacts 54 are openedand contacts 60 are closed. Circuit 48 to cam motor 34 is thusinterrupted, causing the rotation of cam 32 to be held in abeyance atthe point at which the hard spot was encountered. Since contacts 60 wereclosed, circuit 56 is then energized and cam motor 28 is started. Cam 30will be rotated counterclockwise and its high point 66 will engage bar10, moving the bar slightly up and down repeatedly until the drillbreaks through the hard spot. This cyclic action of the drill caused bycam 30 is equivalent to the pecking action normally obtained by anexperienced drill operator. Cam 30 will stop in the position illustratedin Figure 1 during each rotating cycle and will immediately commenceanother rotation cycle as it receives a signal that the hard spot is notbroken through. This signal is provided by the continued energization ofcircuit 56 and deenergization of circuit 48.

When the hard spot is broken through, bar will again be lowered andplunger 36 will again engage feed rate cam 32 so that it is held in thenormal drilling position. Feed rate cam 32 has, during the entirepecking action, remained stationary at the point where the normaldrilling operation was cut off. When plunger 36' again bears the fullsupporting load of bar 10, switch 42 is actuated to open contact 60 andclose contact 54. Cam motor 28 is thus deenergized and cam motor 34 isenergized to continue the interrupted rotation of feed rate cam 32. Thedrilling process then continues as if the hard spot had never beenencountered. Switch 42 may be so constructed that its contacts may notbe reversed unless pecking cam 30 is in the position shown in Figure 1.Thus the pecking cam is kept clear of bar 10 during the normal drillingoperation.

The pecking action of the machine may be repeated any number of timesduring the drilling of the workpiece until the hole being drilled iscompleted. Upon completion of the operation, the operator manually liftslever 10 and supports it on spring 26. Thus switch 52 is opened and theworkpiece may be changed. The operator may also he required to open thehand operating switch 44 as an added safety precaution.

A drilling machine and controls therefor have thus been provided whichwill drill through a workpiece having occasional hard spots and willovercome the hard spots in the manner of an experienced drill operator.The unit provides automatic controls which require a pecking action toovercome hard spots, these controls being initiated only when hard spotsin the workpiece are encountered. Should no hard spots be encountered inany workpiece, feed rate cam 32 will cause the drill to be passed intothe workpiece and removed therefrom in a continuous operation withoutinterruption.

What is claimed is:

1. Control. mechanism for a rotary drill, said mechanism comprising amotor for rotating said drill, a feed rate cam for controlling thelinear feed rate of said drill, a motor for driving said feed rate cam,a first circuit for controlling said rate cam motor, a cyclic cam forintermittently reversing the linear feed direction of said drill, amotor for driving said cyclic cam, a second circuit for controlling saidcyclic cam motor, and means controlling said circuits for energizingsaid first circuit and de-energizing said second circuit under normaldrill operation, said circuit controlling means deenergizing said firstcircuit and energizing said second circuit when the feed rate determinedby said feed rate cam exceeds the actual feed rate of said drill.

2. Drilling mechanism for drilling holes at a predetermined feed rate ina workpiece and including means for overcoming hard spots in saidworkpiece, said mechanism comprising a support lever, a fulcrum for saidlever, counterweights on one end of said lever for substantiallycounterbalancing said mechanism, a drill motor depending from said leveron the opposite side of said fulcrum from said counterweight, a drillrotatably driven by said motor, a feed rate cam for said mechanism, afeed rate cam follower operatively attached to said lever adjacent theend thereof opposite said counterweights and engageable with said feedrate earn, a switch operatively connected to be actuated by movement ofsaid cam follower relative to said lever, said switch having a set ofnormally closed contacts and a set of normally open contacts, a cycliccam operatively positioned beneath said lever for intermittentengagement therewith when said cam is rotated, a cam motor for rotatingsaid feed rate cam, a cam motor for rotating said cyclic cam, a switchactuated by pivotal movement of said lever in a direction to lower saiddrill motor, said last named switch having three sets of normally opencontacts which are closed by said lever pivotal movement, a firstcircuit including one set of contacts of said three-contact switch andthe normally closed contacts of said other switch and said feed rate cammotor,

a second circuit including a second set of contacts of saidthree-contact switch and said normally open contacts of said otherswitch and said cyclic cam motor and a third circuit including the thirdset of contacts of said threecontact switch and said drill motor, saidfirst circuit energizing said feed rate cam motor and said third circuitenergizing said drill motor when said lever is pivoted about saidfulcrum to lower said drill motor, said lever being pivoted about saidfulcrum at a predetermined rate determined by said feed rate cam andsaid cam follower to control the feed rate of said drill, said camfollower supporting substantially the entire unbalanced weight of saidlever and said drill motor, said drill carrying an increased proportionof said unbalanced weight when a hard area in the workpiece beingdrilled is encountered, said cam follower thereby actuating said camfollower switch to reverse said normally closed and said normally opencontacts, thereby deenergizing said first circuit and energizing saidsecond circuit, said feed rate cam motor being thereby deenergized andsaid cyclic cam motor being energized to rotate said cyclic cam toimpart an intermittent up-and-down motion to said drill through saidlever and said drill motor until said hard spot is drilled through, saidcam follower then again supporting substantially the entire unbalancedweight of said lever and said drill motor and reversing said camfollower switch whereby said second circuit is deenergized and saidfirst circuit is energized to continue the drilling operation undercontrol of said feed rate cam.

References Cited in the file of this patent UNITED STATES PATENTS1,911,138 Clute et al May 23, 1933

